Milo g



(No Model.)

M. G. KELLOGG. MULTIPLE SWITOHBOARD.

Patented Oct. 26, 1897 line Jlb.2.,

Line M. 1.

v 3513 abfhgne r 0', wnsmuamu u c the accompanying drawings, forming apart UNTTED STATES PATENT FFICE.

MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGGSVVITCIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

MULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No. 592,322, dated October26, 1897.

Application fil d November 29, 1889. Serial No. 332,025. (No model.)

tiple Switchboards for Telephone-Exchanges, of which the following is afull, clear, concise,

and exact description, reference being had to of this specification.

My invention relates to a single-circuit tele phone system; and itconsists in a system of switching and testing such lines to determinewhether they are in use.

111 the accompanying drawings, illustrating my invention, Figures 1 and1 are front views of sections of two multiple switchboards to which thesame lines are connected. Fig. 2 is a diagram illustrating the main-lineswitchboards, apparatus, and connections necessary to illustrate myinvention. Fig. 3 is a diagram of an operators cord system to be used inconnection with said system. Fig. i is a diagram of asubscribers-station apparatus necessary to illustrate my invention. Fig.5 shows an operators test system to be used at the boards.

In the drawings like parts and apparatus are designated by the sameletters and figures of reference.

G in each case represents a ground connection.

In Fig. 2, A is a sectional View of the switchboard shown in Fig. 1, andA is a sectional View of the switchboard shown in Fig. 1", each asindicated by the line (1 c.

There are as many boards in the exchange as are necessary for the numberof lines. On each board is a spring-jack or similar switch for eachline. Each switch has a contactspring which normally bears on aninsulated contact-point and has a contact-piece insulated from the rest(except by the circuit connections) and is adapted to receive aswitchplug and, when the plug is inserted, to disconnect the spring fromthe contact-point and form connection between the spring and thecontact-piece of the plug.

In Fig. 2, g 9 represent the springs of the different switches, h h thecontact-points on which the springs normally bear, and j j the insulatedcontact-pieces. Z Z are the switch holes. ab are the rubber strips onwhich the metal parts are mounted, as shown, and through the fronts ofwhich are the holes I Z. These holes are adapted to receive theswitchplugs, (shown in Fig. 3 and marked D D,) and when a plug isinserted into a switch it operates it, as above described. Thecontactpieces jj should be so placed that atest-plug may be readilyapplied to them. Theironly function is to form test-pieces for theirlines, and they may be placed as shown or in any convenient positions ontheir boards.

The connection of a line to the switchboards is as follows and as shown:A line normally grounded at the central office passes successivelythrough the pairs of contactpoints of its switches on the severalboards, passing in each case to the spring first. It then passes throughits ann unciator and a resistancecoil to ground.

w is the annunciator, and 0c is the resistancecoil.

The contact-pieces jj of the line are connected to the line, theconnection being between the switches and the resistance of theannunciator and resistance-coil. In lines which are normally open to theground at the central office the line, after passing through thecontact-points of its switches,is connected to the contact-pieces jj ofits switches. Independent calling-circuits are generally used for suchlines, such as the Law and American district systems. Line No.1,asmarked, shows the connection of a line normally grounded, and line N o.2 the connection of one normally open at the central office.

Fig. 3 shows an operators cord system with one pair of cords and theirplugs, switch, annunciator, and operators telephone and bat tery orgenerator. The plugs D D are con structed substantially as shownmz mbeing the rubber insulations and n n the contact-pieces, and they shouldbe inserted into the switches in such a position that the contact-pieceof the plug forms connection with the contactspring of the switch and isnot in connection with the oontact-piecej. 0 is a metal strip on whichthe bases of the plugs normally rest, and which then connects thecontact-pieces of the plugs with the ground. y is the looping-in switchof the pair of cords. r is the clearing-out annunciator. tis theoperators telephone, and B is her calling-generator. The circuits are asshown.

The method of connecting other pairs of cords, with their accompanyingapparatus, to the system, and the method of operating the system inconnection with the switchboards, will be apparent to those skilled inthe art.

Each operator has one cord system, with as many pairs of cords as shemay need, and the parts are conveniently mounted and arranged for herwork.

In the subscribers-station apparatus shown in Fig. 4, 1 is themagneto-bell, containing a switched-from the circuit of the line whenthe telephone is placed on the switch.

In the operators test system shown in Fig.

5, T is the test-plug, S is the test receiving instrument, B is thetest-battery, and G is the ground connection. Each operator has one testsystem, and the parts are connected substantially as shown and areconveniently mounted for the operation of the system. The test receivinginstrument and battery should be so adjusted to each other and to thecircuits that the instrument will respond or sound when the test-plug isplaced on a test' contact-piece j of a line and the subscriberstelephone is on its switch and the circuit to,

the line is not opened by the line being switched at one of the boards,but will not sound when the line is switched or when the resistance isintroduced into the circuit at the subscribers station by the operatorstele-,

phone being switched for use. The resistance of the office groundconnection of the line through the annunciator and resistance-coilshould be-made large enough so as not to produce enough current throughthe test receiving instrument to operate it when the line and thesubscribers telephone are not switched,as above indicated, or to operatethe annunciator when the test is made. resistance will depend on theform and construction of the other parts. The annunciator-magnet mightin cases be constructed with sufficient resistance so that no other coilwould be required. The resistance at the subscribers station, which isintroducedinto the circuit of the line when his telephone is switchedfor use, should be sufficiently great so that the resistance of the lineis then increased, so that the test receiving instrument will not thenoperate on the test being made.

The amount of this The condenser bridges this resistance, so that thetelephone-currents are not unduly impeded. The resistance bridges thecondenser, so that the circuit will not be opened to calling-currentssent over it when the subscribers telephone is switched for useas,forinstance, a clearing-out signal made by the other subscriber.

The system of testing is as follows: An operator, on testing, places thecontact-piece T ofher test system on the contact-piece j of the line tobe tested. If the line is not switched at any board, a complete circuitis established from the ground through the test receiving instrument tothe line and to ground at the subscribers station. If his telephone ison its switch, the resistance of thecircuit will be sufficientlylowsothat the test receiving instrument will sound, showing that the line isfree. If, however, the telephoneis switched for use, the resistance ofthe line is increased by the introduction of resistance, so that theinstrument will not sound; and if the line is switched for use at thecentral oflice the testcircuitis'interrupted, so that the test receivinginstrument will not sound. \Vhen an operator makes a test and receivesno response or sound, she therefore knows that the line is in use,either by the telephone being switched for use or by the line beingswitched for use, and she will not switch it with another line. I

The test system depends on the fact that an electromagnet, with anarmature and a retractile spring acting on the armature, may

readily be made to move or attract the armature when in closed circuitwith a battery be obtained. When the test is made, as above described,and neither the line is switched for use nor the subscribers telephoneis switched for use,the test-circuit is from the office ground throughthe test-battery and test receiving instrument to the contact to whichthe plug is applied, thence to ground in two derived circuits, onethrough the resistance-coil of relatively high resistance at the centraloffice and the other through the circuit of the nor mally closed pairsof contacts of the line to the ground at the subscribers station. Thetest receiving instruments are so adjusted to the circuits and thebattery that when the line is neither switched nor the subscriberstelephone is switched for use the instrumentwill sound or respond. Itis, however, so adjusted that either when the line is switched forconversation and the derived circuit to ground at the subscribersstation is thereby opened or the subscribefls telephone is switched foruse, in either case increasing the resistance of the derived circuit inwhich they are included, and therefore increasing the resistance of theclosed circuit in which the test instrument and battery are included,there will not be sufficient current passing through the instrument tocause it to be operated, al-

though there will be some current passing through it, which will tend tocauseit to operate. This test system therefore depends on a marginaladjustment of these parts to each other and to the resistances to securethe sounding of the test receiving instrument when neither the line northe subscribers telephone is switched for use and to insure that it doesnot sound when either is switched for use. V

The resistance-coil furnishes the additional resistance required in thecircuit when the subscribers telephone is switched for use to providefor the marginal adjustment and operation of the test system asdescribed, while the condenser provides an easy circuit or path for thepassage of the telephone-currents. The resistance-coil moreover providesan all metallic circuit through the subscribers line for the passage ofthe clearing-out eurrents,especially when one subscriber sends theclearing'out signal while the other subscriber has not yet placed histelephone on his switch, as may often be the case.

IVith the forms of apparatus used in telephone-exchanges theclearing-out signal will be readily operated over the resistancesnecessary to produce the marginal adjustment of the test system whichhas been so described.

In multiple-switchboard systems an operator to whom certain lines areassigned to answer frequently receives several calls at practically thesame moment, and it may require some time before she can switch to aline and answer its call. In systems which depend only on the switchingof the line at some other board another operator may in the meantimetest the line, and, finding it to test free, may switch it to anotherline and cause annoyance and confusion to the subscriber. I11 thissystem the trouble is obviated, because as soon as the subscriber takeshis telephone from its switch the line will test busy whether or not itis switched at the central office. Again, in systems of testing whichdepend only on the subscribers telephone being on or off its switchconfusion frequently occurs from the fact that a subscriber places histelephone on its switch without sending in a clearing-out signal, andhis line tests free and is connected to when it is already switched atthe central office with some other line. Lines in this condition aretechnically called tied up. In this system again this trouble isobviated, because the line will test busy until it is disconnected atthe central olhcc, whether or not the subseribers telephone is switchedfor use. The system therefore combines the advantages and obviates thedisadvantages of the two general systems of testing outlined above.

The line-annunciators will be so related to the test-batteries that theywill not be made to indicate when an annunciator and battery are closedto each other on a test being made. For this purpose the annunciatorsmay be polarized and so connected with reference to the batteries thatthe batteries will not opcrate them, or they may not be of sufficientlysensitive construction to be operated by the test-batteries.

I claim as myinvention and desire to secure by Letters Patent- 1.Atest-circuit for a subscribers line,from the office ground through atest receiving instrument and battery to a test contact-plug, and thenceto a line-contact when the test is applied; thence in one direction tothe office ground through a comparatively high resistance, and in theother direction to the subscribers ground through a pair of switchcontact-points in the central oflice and the subscribers-stationapparatus; in combination with a switch-plug which separates said pairof contact-points while it switches the line, and a switch apparatus andcircuits at the subscribers station to switch apparatus of comparativelyhigh resistance shunted by a condenser into the circuit of line when thetelephone is switched for use, and low resistance when it is not thusswitched, said test receiving instrument being adjusted to respond tocurrent of certain strength, but not to respond to current ofconsiderably less strength, and said instrument and battery beingadjusted to each other and to the said several resistances and thecircuits to the degree that the instrument sounds when, on the testbeing made, neither the telephone nor the line is switched for use andnot otherwise, substantially as set forth.

2. A test-circuit for a subscribers line, from the office ground througha test receiving instrument and battery to a test contact-plug, andthence to a line-contact when the test is applied, thence in onedirection to the offiee ground through a comparatively high resistanceand in the other direction to the sub seribers ground through a seriesof pairs of switch contact-points, one on each of several boards, incombination with switch-plugs adapted to be inserted into the switchesfor switching and when a plug is inserted into a switch to separate itssaid pair of contact points while the line is thus switched for use, anda switch apparatus and circuits at the subscribers station to switchapparatus of comparatively high resistance shunted by a condenser intothe line-circuit while his telephone is switched for use, and ofcomparatively low resistance while it is not thus switched, saidinstrument being adj ustcd to respond to currentof certain strength, butnot to respond to current of considerably less strength, and saidinstrument and battery being adjusted to each other and to said severalresistances and the circuits to the degree that the instrument soundswhen, on the test being made, neither the telephone nor the line isswitched for use, but not otherwise, substantially as set forth.

3. A test-circuit for a subscribers line,from the office ground througha test receiving instrument to a test contact-plug, and thence to a linecontact-point when the test is applied, thence in one direction to theoftice ground through a comparatively high resistance, and in the otherdirection to the subscribers ground through a pair of switchcontactpoints in the central oflice and the subscribers-stationapparatus, and a battery in the circuit, in combination with aswitch-plug adapted to be inserted into the switch and when inserted toseparate the contact-points while the line is switched for use, and aswitch apparatus and circuits at the subscribers station toswitchapparatus of comparatively high resistance shunted by a condenser intothe circuit 01": the line when the telephone is switched for use, and ofcomparatively loW resistance'when it is not thus switched, said testinstrument being adjusted to respond to current of certain strength, butnotto respond to current of considerably less strength, and saidinstrument and battery being adjusted to each other and to said severalresistances and the circuits to the degree that the instrument soundswhen, on the test being made, neither the telephone nor the line isswitched for use, and not otherwise, substantially as set forth.

4. In a telephone-exchange system, a subscribers line grounded at itsouter end and having in its circuit, in the station apparatus, acomparatively high resistance shunted by a condenser, while histelephone is switched for use, and a comparatively low resistance Whileit is not thus switched, a switch at the central office having a pair ofcontact-points normally in contact but separated while the line isthereby switched for use, and a test contact-piece insulated from therest, except by the circuit connections, said line passing through saidpair of contact-points, and thence to said test contact-piece, incombination with a resistance-coil grounded on one side and connected onthe other side to the line-circuit between the contact-points and thetest contact-piece, and a test receiving instrument with batterygrounded on one side and connected on its other side to a testplug ordevice adapted, at the will of the operator, to be brought intoconnection with said test contact-piece, said instrument being adjustedto respond to current of certain strength, but not to respond to currentof considerably less strength, and said instrument being adjusted to thebattery and said several resistances and the circuits to the degree thatit sounds when, on the test being made, neither the subscriberstelephone nor the line is switched for use and not otherwise,substantially as set forth.

condenser while his telephone is switched for use, and a comparativelylow resistance while the telephone is not thus switched, a series ofswitches at the central office for said line, one switch on each ofseveral boards, each having a pair of contact-points normally incontact, but separated while the line is thereby switched, and a testcontact-piece insulated from the rest (except by the circuitconnections), said line passing successively through its said pair ofcontact-points, and thence to said test contact-piece, in combinationwith a resistance-coil grounded. on one side and connected on its otherside to the line after it has passed through said-pairs ofcontact-points, and a test wire or circuit containing a test receivinginstrument and battery, grounded on one side and connected on its otherside to a test plug or device adapted, at the will of the operator, tobe brought into connection with said test contact-piece, said instrumentbeing adjusted to respond to current of certain strength, but not torespond to current of considerably less strength and said instrumentbeing adjusted to the battery and said several resistances and thecircuits to the degree that it sounds when, on the test being made,neither the subscribers telephone nor the line is switched for use, butnot otherwise, substantially as set forth.

6. In a telephone-exchange system, a subscribers line grounded at itsouter end and having in its circuit at his station, apparatus ofcomparatively high resistance shunted by a condenser while his telephoneis switched for use, and comparatively low resistance while it is notthus switched, in combination with a series of test contact-pieces, onepiece on each of several boards and normally connected to the line,switch contact -points which disconnect the line from its saidcontact-pieces while it is switched for use, a resistance-coi1 connectedon one side to said contact; pieces and grounded on the other side, incombination with test receiving instruments,'one at each board, eachgrounded on one side and connected on its other side to a test-plugadapted to be brought for testing into connection with the testcontactpiece at its board, said instrument being adjusted to respond tocurrent of certain strength, but not to respond to current ofconsiderably less strength, and said instrument being connected incircuit with a battery and adjusted to it and said several re sistancesand the circuits to the degree that it will sound when, on the testbeing made, neither said telephone nor the line is switched for use andnot otherwise, substantially as set forth. a

7. In a telephoneexchange system, a subscribers line grounded at itsouter end and having in its circuit at his station, apparatus ofcomparatively high resistance shunted by a condenser, while histelephone is switched for use, and comparatively low resistance whilethe telephone is not thus switched, multiple switchboards, switches forthe line, each having a pair of contact-points normally closed but openwhile the line is switched at its board, test contact-pieces, one oneach board, and a resistance-coil grounded on one side, said linepassing successively through said pairs of contact-points and thenceconnected to said test contact-pieces and to the other side of saidresistance-coil, in combination with test receiving instruments, one ateach board, grounded on one side and connected on its other side to atest plug or device adapted to be brought for testing into connectionwith the test contact-piece at its board, said instrument being adjustedto respond to current of certain strength, butnot to respond to currentof considerably less strength, and said instrument having a battery incircuit with it and adjusted to the battery and said several resistancesand the circuits to the degree that it will sound when, on a test beingmade, neither said telephone nor the line is switched for use, and nototherwise, substantially as set forth.

MILO G. KELLOGG. WVi tnesses FRANCES D. KELLOGG, MARGARETHA RIEHL.

